Fix demo mode and add a test to run demo

I've extracted the main functionality into the `run` function so that this can
be tested without triggering the `System/exit` in `-main`.

deps.edn

@@ -1,4 +1,4 @@
-{:paths ["src" "resources" "private"]  ;; Private is not include in the build
+{:paths ["src" "resources" "private"]  ;; Private is not included in the build
  :deps {
         org.clojure/clojure {:mvn/version "1.11.1"}
         org.clojure/data.csv {:mvn/version "1.0.1"}

src/core.clj

@@ -48,23 +48,14 @@
   (set/difference (set (keys projects)) (->> records (map :name) set)))
 
 (def demo-options
-  {:csv (io/resource "example-paychex-pay-item-details.csv")
+  {:csv (io/resource "example-paychex-pay-item-details-2025.csv")
    :date "2024-01-01"
    :period "January 2024"
    :total-fees 66.67M})
 
-(defn -main [& args]
-  (let [{:keys [options errors summary]} (parse-opts args cli-options)
-        options (if (:demo options) (merge options demo-options) options)]
-    (when (:help options)
-      (println summary)
-      (System/exit 0))
-    (when errors
-      (println
-       (str "The following errors occurred:\n\n"
-            (str/join \newline errors)))
-      (System/exit 1))
-    (let [{:keys [date period pay-receipt-no pay-invoice-no total-fees project]} options
+(defn run [options]
+  (let [options (if (:demo options) (merge options demo-options) options)
+        {:keys [date period pay-receipt-no pay-invoice-no total-fees project]} options
         {:keys [fees-receipt-no fees-invoice-no retirement-receipt-no retirement-invoice-no]} options
         records (import/read-csv (:csv options))
         imported (concat (import/net-pay date period pay-invoice-no project records)
@@ -75,13 +66,25 @@
                          (import/fees date period fees-receipt-no fees-invoice-no total-fees project records)
                          (import/retirement date period retirement-receipt-no retirement-invoice-no records))
         unmatched (unmatched-employees records project)]
-      (when-not (empty? unmatched)
+    (when (seq unmatched)
       (println
        (str "Could not find these employees in the payroll:\n\n"
             (str/join ", " unmatched)))
       (System/exit 1))
     (doseq [i imported]
-        (println (import/render-transaction i))))))
+      (println (import/render-transaction i)))))
+
+(defn -main [& args]
+  (let [{:keys [options errors summary]} (parse-opts args cli-options)]
+    (when (:help options)
+      (println summary)
+      (System/exit 0))
+    (when errors
+      (println
+       (str "The following errors occurred:\n\n"
+            (str/join \newline errors)))
+      (System/exit 1))
+    (run options)))
 
 (comment
   ;; Examples to exercise the importer during development.

test/core_test.clj

@@ -0,0 +1,8 @@
+(ns core-test
+  (:require [core]
+            [clojure.test :as t :refer [deftest is]]
+            [clojure.string :as str]))
+
+(deftest demo-produces-output
+  (let [output (with-out-str (core/run {:demo true}))]
+    (is (not (str/blank? output)))))